DESCRIPTION: The long-term objectives are to identify the optical signals that specify focus of the eye, and that control reflex accommodation and the process of emmetropization (the coordination of growth and development to minimize myopia and hyperopia), and to identify the visual mechanisms that mediate the optical signals. Two hypotheses will be examined: First, that ocular focus is specified by the relative contrast of spectral components of the retinal image that have the same spatial frequency and the same spatial phase; and that three cone classes (L-, M- and S-) analyze the chromatic signals. Second, that the angle of incidence of light forming the margins of the blur spread-function also specifies focus and drives accommodation. Accommodation will be monitored continuously under open-loop (pinhole) conditions to simulated step changes in defocus (including longitudinal chromatic aberration) on the contrast of spectral components (red, green, blue) of the retinal image having the same spatial frequency. The spatial phase of the red and blue components of grating images (2 to 6 c/d) will be phase-shifted with respect to the green component (5 arc min to 20 arc min) to determine the degree to which the spectral components must have similar spatial phases in order to drive accommodation. Another experiment will determine whether S-cones play a role, by driving accommodation with and without a narrowband blue "wash" of veiling luminance (440 nm) superimposed over the grating target to minimize S-cone activity. To test the second hypothesis, accommodation will be driven by step and ramp simulations of monochromatic (550 nm) defocussed edge spread-functions while the angle of incidence of rays forming the blurred retinal image is controlled by a moveable pinhole (0.75 mm) pupil. Next, a computer-controlled LCD array will be imaged in the plane of the subject's pupil to measure and alter the Stiles-Crawford effect Type I. The LCD array will image an apodizing pupil in the subject's natural pupil to neutralize and reverse the asymmetry of the S-C function, while stationary (O D and 5 D for 40 seconds) and moving gratings (0.2 Hz, 1 - 3 D, 3 c/d) drive accommodation. Finally, ramp simulations of defocus blur will be viewed through a moving pinhole pupil with the decentered Stiles-Crawford effect neutralized and reversed to determine whether the retina monitors the angle of incidence of light per se , or whether the "brightness" effect from the decentered S-C function (decentered blur centroid) plays a role in specifying focus and controlling accommodation.